Electricity demand calculation

Electricity demand is built in the same way as heat demand: from consumer types with monthly values and 168-hour weekly profiles. A measured load profile can be imported in addition. Unlike on the heat side, however, EPOS-Plan calculates electricity not in hours but in quarter hours – for reasons that are directly connected with the assessment of self-consumption and storage operation.

This page describes the working sequence in the program. The origin and structure of the load profiles are described by the fundamentals page Electricity demand and load profiles; where the step sits in the overall sequence is shown by the Program workflow overview. Electricity demand is only recorded if the building blocks electricity consumers or electrical load profile are activated in the project.

Contents of this page

Consumer types and weekly profiles

You select a consumer type from the catalogue and enter the annual consumption; the distribution over the year is taken care of by the stored monthly values and the weekly profile with 168 hourly values. The annual consumption is therefore the only figure you have to know; the type supplies the time structure.

Several consumer types can be kept side by side; the total demand of the object results from their sum. That is the way to model different uses separately instead of merging them into a single annual figure. As with all catalogue components, a project-specific copy is created on assignment: adapted values stay in the project and do not change the catalogue.

Monthly values and weekly profile follow the same pattern as on the heat side; their editing in the profile editor is described by the subpage Heat demand calculation.

Calculating in quarter-hourly values

For self-consumption studies the hourly resolution is too coarse: self-consumption and storage management come out too favourable in hourly averages, because short load peaks and generation peaks cancel each other out arithmetically within one hour although they do not coincide in time at all. EPOS-Plan therefore converts the profile to quarter hours and works internally with 35,040 values per year.

This resolution is not a question of presentation but of reliability: it decides which share of your own generation arithmetically stays in the object and which share is fed into the grid – and thus the assessment described on the subpage Revenue calculation.

Importing a measured load profile

Measured load profiles can be imported and are fitted automatically according to their time raster – hourly or quarter-hourly values – and superimposed on the calculated profile. The two routes therefore do not exclude each other: you can combine the measured load profile of an existing part of the operation with the type profiles of further consumers, for instance where an extension is planned for which no measurement can exist yet.

Result of the calculation

The results available are the maximum power demand, the annual consumption, the monthly values and the sorted load duration curve. The maximum value is the quantity a demand price depends on; the load duration curve shows for how many hours in the year a given output is exceeded, and thus how far own generation can carry at all.

This demand is the demand of the object. In the simulation the consumption of the heat generators is added later – above all heat pump and back-up heater – while CHP electricity, photovoltaics and storage discharge are subtracted; what remains is grid supply, negative values are feed-in.

Notes for practice

Where a measured quarter-hourly load profile is available, it is the most reliable input you can bring into a project – considerably more reliable than any type profile. Ask the network operator or the supplier for it before working with catalogue profiles; for industrial and commercial objects with demand metering it is usually available.

Check the annual consumption against the electricity bill and the maximum value against the billed peak demand. If annual total and peak match, the distribution in between is usually usable as well; if they deviate, a different consumer type helps more than adjusting the annual figure.

When comparing with third-party evaluations, bear in mind that hourly and quarter-hourly calculations give different results: self-consumption ratios derived from hourly averages come out systematically too high. And a high electricity demand at the right time is worth more for the economics of a photovoltaic system than a high annual consumption – which is why it is worth looking at the profile and not only at the total.

How things continue is shown by the Program workflow overview; before this step lie Project management and the Heat demand calculation, after it follow Revenue calculation and Economic analysis. The engineering background is collected under Fundamentals › Electricity demand and load profiles, Photovoltaics and Battery storage, worked cases under Examples.